This invention relates to improvements in a light emitting device capable of emitting multiple colors suitable for application for example in organic electro-luminescence(=EL) devices.
The art of combining a reflective layer with a multi-layer dielectric film wherein layers having differing refractive indexes are alternately stacked, and therewith reflecting light of specific wavelengths is known. In Shingaku Gihou, OME 94-79 (March, 1995), pp 7-12, the concept is set forth of using very small resonance structures based on such multi-layer dielectric films to emit multiple light colors. According to this literature, by adjusting the positions of the light emission layer and the reflective surface where reflection occurs in these very small resonance structures, resonant light can be output having any of the wavelengths contained in the light output by the emission layers.
In Japanese Patent Laid-open No. 275381/1994, for example, a light emitting device having the layer structure illustrated in FIG. 13 is disclosed. This light emitting device comprises a transparent substrate 100, a very small resonance structure 102, a positive electrode 103, a hole transport layer 106, an organic EL layer 104, and negative electrodes 105. The wavelengths are selected by altering each of the thicknesses of the positive electrodes 103.
In the article written by members of Bell laboratory, J. Appl. Phys. 80(12), Dec. 15, 1996, a light emitting device having the layer structure illustrated in FIG. 14 is disclosed. This light emitting device comprises a transparent substrate 100, a very small resonance structure 102, SiO2 film 108, a positive electrode 103, a hole transport layer 106, an organic EL layer 104, and negative electrodes 105. The thicknesses of the negative electrodes 103 are the same, but the optical path lengths are altered, respectively, by an SiO2 layer, to select the resonant light wavelength.
With light emitting devices having the structure set forth in the publicized literature noted above, however, there is a problem in that it is very difficult to design light emitting devices optimized for all of a plurality of wavelengths. In other words, the very small resonance structure and gap adjustment materials are optimized for a specific wavelength dispersion. Wherefore, with a very small resonance structure designed so that it is compatible with one of the plurality of light colors having a range of wavelengths, adequate reflectance cannot be achieved relative to other wavelength dispersions. In a color display apparatus, for example, it is necessary to balance the resonance intensity and color purity of each of the colors R (red), G (green), and B (blue) according to the characteristics of human vision. Such balancing adjustments are difficult with conventional light emitting devices.
That having been said, it is nevertheless very difficult in actual manufacturing practice to make the structure of the multi-layer dielectric film different for each pixel (light emission region) unit, therefor this is a difficult method to realise industrially, and hence an expensive process.
Thereupon, a first object of the present invention is to provide a multiple wavelength light emitting device that is balanced and optimized for a plurality of wavelengths.
A second object of the present invention is to provide a multiple wavelength light emitting device wherewith optimization for a plurality of wavelengths is easy, and the manufacture thereof is easy.
A third object of the present invention is to provide an electronic apparatus capable of emitting light of a plurality of optimized wavelengths.
A fourth object of the present invention is to provide an interference mirror capable of sharpening and emitting a multiple wavelength light spectrum.
An invention that realizes the first object noted above is a multiple wavelength light emitting device for emitting multiple light beams having differing wavelengths, comprising:
1) light emission means for emitting light containing the wavelength components to be output;
2) a reflecting layer positioned in proximity to the light emission means; and
3) a semi-reflecting layer group that is positioned so as to be in opposition with the reflecting layer with the light emission means sandwiched therebetween, wherein semi-reflecting layers that reflect some of the light emitted from the light emission means having specific wavelengths, while transmitting the remainder, are stacked up in order in the direction of light travel corresponding to the light wavelengths to be output.
The present invention is also a multiple wavelength light emitting device that comprises at least two but possibly more light emission regions such that the wavelengths of the output light differ, structured so that the distance between a reflecting surface for light from the light emission means side on the semi-reflecting layers that reflect some of the light output from one of the plurality of light emission regions and a point that exists in the interval from the end of the light emission means on the semi-reflecting layer group side to the reflecting layer is adjusted so that it becomes an optical path length at which light of the wavelength output from that light emission region resonates.
Based on the structure described above, the semi-reflecting layer group is optimized for all light wavelengths that are to be emitted, in any of the light emission regions. By adjusting the distance between the reflecting surface of the semi-reflecting layers for the light from the light emission means side and the point existing in the interval from the end of the semi-reflecting layer group side of the light emission means to the reflecting layer, and preferably the distance between the light emission points within the light emission means and the surface (reflecting surface) on the light emission means side of the reflecting layer, according to the light emission means and reflecting layer used, which optimized light is output is determined. The semi-reflecting layers other than those optimized for light of wavelengths other than those output merely function commonly as semitransparent layers exhibiting a certain attenuation factor, wherefore it is possible to maintain balance between light of multiple wavelengths.
There is no limitation on the xe2x80x9clight emission means,xe2x80x9d as used here, but it is at least necessary that the wavelength component be generated for the light that one wishes to output. The xe2x80x9creflective layerxe2x80x9d should form a flat surface, but it does not necessarily have to have a uniform flat surface. The language xe2x80x9cin proximity toxe2x80x9d includes cases where there is contact with the light emission means, and cases where the positioning results in a slight gap therebetween. So long as a reflective action is exhibited, this may be something that is not closely and indivisibly connected to the light emission means. The xe2x80x9clight emission regionxe2x80x9d is a domain for outputting light having some wavelength dispersion, and signifies that light of different wavelengths is output in each light emission region. xe2x80x9cWavelengthxe2x80x9d is inclusive of a wide range of wavelengths, including ultraviolet and infrared radiation in addition to wavelengths in the visible light region. xe2x80x9cSemi-reflecting layersxe2x80x9d include structures such as half mirrors or polarizing panels in addition to interfering laminar structures wherein multiple film layers having different refractive indexes are stacked in layers. In the case of a very small dielectric-based resonating structure, xe2x80x9creflecting surfacexe2x80x9d refers to the surface on the side toward the light emission means. xe2x80x9cOptical path lengthxe2x80x9d corresponds to the product of the medium""s refractive index and thickness.
The specification of the xe2x80x9cpoint existing in the interval from the semi-reflecting layer group side of the light emission means to the surface of the reflecting layerxe2x80x9d is for the purpose of adjusting the position in the thickness direction where resonance conditions will be satisfied by the light emission means configuration. Here, the positional relationship in the thickness direction (light axis) is defined, and a plane that emits light or reflects light (in the case of a reflecting layer) is formed by the set of xe2x80x9cpointsxe2x80x9d that satisfy the resonance conditions in the light emission means overall. Here, when the point existing in the interval from the end of the light emission means on the semi-reflecting layer group side to the reflecting layer is on the reflecting surface of the reflecting layer, the distance L between the reflecting surface on the light emission means side in the semi-reflecting layer of the plurality of semi-reflecting layers that reflects light of wavelength xcex, in the light emission region wherein light of wavelength xcex is output, and the point existing in the interval from the end of the semi-reflecting group side in the light emission means to the surface of the reflecting layer is adjusted so as to satisfy the relationship
L=xcexa3dixe2x80x83xe2x80x83Eq. 1
xcexa3(nixc2x7di)+m1xc2x7("PHgr"/2xcfx80)xc2x7xcex=m2xc2x7xcex/2
where ni is the refractive index of the i""th substance between the semi-reflecting layer and the light emitting surface, di is the thickness thereof, "PHgr" is the phase shift occurring at the reflecting surface in the reflecting layer, and m1 and m2 are natural numbers. L corresponds to the actual distance, while xcexa3 (nixc2x7di) corresponds to the optical path length. It is a necessary condition for resonance between the semi-reflecting surface and the reflecting surface placed on the side opposite thereto that the sum of the optical path length and the phase shift be a natural multiple of the half-wavelength.
There are also cases where a resonance condition is set, setting the point in the interval from the end of the light emission means on the semi-reflecting layer group side to the reflecting layer as the light emission point in the light emission means. In such cases as this, the distance L between the reflecting surface on the light emission means side in the semi-reflecting layer of the plurality of semi-reflecting layers that reflects light of wavelength xcex, in the light emission region wherein light of wavelength xcex is output, and the point existing in the interval from the end of the semi-reflecting group side in the light emission means to the surface of the reflecting layer is adjusted so as to satisfy the relationship
L=xcexa3dixe2x80x83xe2x80x83Eq. 2
xcexa3(nixc2x7di)=m2xc2x7xcex/2+(2m3+1)xc2x7xcex/4
where ni is the refractive index of the i""th substance between the reflective surface and the point, di is the thickness thereof, m2 is a natural number, and m3 is an integer greater than 0.
The semi-reflecting layer group here is placed evenly so that multiple types of semi-reflecting layers having differing wavelengths corresponding to the plurality of light wavelengths are not separated by a light emission region. The reflecting surface for the light from the light emission means side of the semi-reflecting layer in the semi-reflecting layer group is in a different position in the thickness direction for each light emission region having a different light emission wavelength.
It is to be preferred that the semi-reflecting layer group be arranged so that the semi-reflecting layer reflecting light of longer wavelength is on the side nearer to the light emitting device. This is because it is harder for light of short wavelength to be reflected by a semi-reflecting layer optimized for light of longer wavelength.
More specifically, the semi-reflecting layers making up the semi-reflecting layer group are configured such that two layers of differing refractive index are stacked up alternately. If we have two semi-reflecting layers having different refractive indexes, for example, and take n1 as the refractive index of one layer, d1 as the thickness thereof, n2 as the refractive index of the other layer, and d2 as the thickness thereof, then, when the wavelength of the light reflected in that semi-reflecting layer is xcex and m is made 0 or a natural number, then an adjustment is made to satisfy the relationship
xe2x80x83n1xc2x7d1=n2xc2x7d2=(xc2xc+m/2)xc2x7xcexxe2x80x83xe2x80x83Eq. 3
This is an interference condition in this resonance structure. It corresponds to the half-wavelength in one combination of two layers. Reflection occurs when light from a layer of low refractive index is incident on a layer of high refractive index, wherefore it is desirable that the arrangement be high refractive index) layer, low layer, high layer, low layer, etc., stacking from the light emission means.
In the invention that realizes the second object noted above, the distance from the reflecting surface for light from the light emission means side of the semi-reflecting layer closest to the light emission means to a point existing in the interval from the end of the light emission means on the semi-reflecting layer group side to the reflecting layer, and preferably the distance from the light emission point in the light emission means and the surface on the light emission means side of the reflecting layer, according to light emission means and reflecting layer used, are maintained at optical path lengths that satisfy Equations 1 and 2 above. And a gap adjustment layer is comprised, between the semi-reflecting layers, for adjusting the distance between the reflecting surface for light from the light emission means side in a semi-reflecting layer other than the semi-reflecting layer closest to the light emission means and the point existing in the interval from the end of the light emission means on the semi-reflecting layer group side to the reflecting layer. The light emission means can be provided flat, without making the height thereof different in the thickness direction, wherefore the complex process of changing the layer thickness in each light emission region during manufacture can be omitted. The xe2x80x9cgap adjustment meansxe2x80x9d need only exhibit light transmissivity, and may be freely selected from among resins or dielectric materials.
In the present invention, moreover, the distance from the reflecting surface for light from the light emission means side of the semi-reflecting layer closest to the light emission means to a point existing in the interval from the end of the light emission means on the semi-reflecting layer group side to the reflecting layer, and preferably the distance from the light emission point in the light emission means and the surface on the light emission means side of the reflecting layer, according to light emission means and reflecting layer used, are maintained at lengths that satisfy Equations 1 and 2 above. And, in order to adjust the distance between the reflecting surface for light from the light emission means side in a semi-reflecting layer other than the semi-reflecting layer closest to the light emission means and the point existing in the interval from the end of the light emission means on the semi-reflecting layer group side to the reflecting layer, the thickness of one layer, in the laminar structure configuring the semi-reflecting layers wherein layers of different refractive index are stacked up, is altered. The gap is adjusted at the layer at the boundary with the semi-reflecting layer, wherefore the quantity of materials used can be cut back, and it is only necessary, in terms of fabrication process, to control the film thickness when forming the layer the thickness thereof is to be adjusted, so the fabrication process can be omitted. It is preferable that the layer used for adjusting the thickness be the layer of high refractive index that is closest among the semi-reflecting layers to the light emission means.
In one aspect of the light emission means, multiple types of light emission means that emit a relatively large number of light components having wavelengths associated with light emission regions are provided so that they are associated with the light emission regions. This applies to cases where optimal light emitting materials are used which contain the wavelength components for the light output in each light emission region.
In another aspect of the light emission means, light emission means are provided, common to each light emission region, capable of emitting light including all components of wavelengths associated with the light emission regions. If light emitting materials can be used which contain all of the light wavelength components to be output, then there is no need to prepare different light emitting material in each light emitting region.
In concrete terms, the light emission means may comprise an organic electro-luminescence layer sandwiched between electrode layers, wherein the electrode provided at the back surface thereof corresponds to the reflection layer. In an organic electro-luminescence layer such as this, there are cases where the point where the electric field reaches maximum between the electrodes coincides with the light emission point in the light emitting layer. It is preferable here that the light emission means be provided with a hole transport layer on the side toward the positive electrode. The light emission means may also be provided with an electron transport layer on the side of the organic electro-luminescence layer toward the negative electrode.
When an organic electro-luminescence device is used, the distance between the reflecting surface for light from the light emission means side of the semi-reflecting layers and a point existing in the interval from the end of the light emission means on the semi-reflecting layer side to the reflecting layer is adjusted by the thickness of the positive electrode located on the semi-reflecting layer group side of the light emission means.
When an organic electro-luminescence device is used, moreover, a layer for adjusting the distance between the reflecting surface for light from the light emission means side of the semi-reflecting layers and a point existing in the interval from the end of the light emission means on the semi-reflecting layer side to the reflecting layer (such as a hole transport layer) may be provided on the side of the light emission means toward the semi-reflecting layer group.
The negative electrode is configured of a material exhibiting light reflectance. If some degree of light reflectance is exhibited, then it can be used as a reflecting surface for the semi-reflecting layer.
When the configuration is made to enable light emission by the light emission region, at least one or other of the electrode films sandwiching the organic electro-luminescence layers is formed separately and independently in correspondence with the light emission region. If one or other of the electrode layers is separated, an active matrix drive configuration is formed, whereas if both electrodes are separated, a passive matrix drive configuration is formed.
In terms of a concrete aspect, it is desirable that the electrodes be separated by a partitioning material and, if necessary, that the organic electro-luminescence layer also be partitioned off. Such a partitioning material would consist of an insulator material.
In another possible aspect, of the electrode films, the negative electrode is made to correspond to the light emission region and separated, while the positive electrode, in order to adjust the distance from the reflecting surface for light from the light emission means side of the semi-reflecting layer closest to the light emission means to a point existing in the interval from the end of the light emission means on the semi-reflecting layer group side to the reflecting layer, has the thickness thereof changed and made to correspond to the light emission region.
In yet another possible aspect, of the electrode films, the positive electrode is made to correspond to the light emission region and separated, and also, in order to adjust the distance from the reflecting surface for light from the light emission means side of the semi-reflecting layer closest to the light emission means to a point existing in the interval from the end of the light emission means on the semi-reflecting layer group side to the reflecting layer, has the thickness thereof changed and made to correspond to the light emission region.
When such independent electrodes are provided, drive circuits are provided separately for driving the electrically separated electrode films.
An invention that realizes the third object noted above is an electronic apparatus that is equipped with the multiple wavelength light emitting device of the present invention, as described in the foregoing. One possible concrete aspect thereof is an electronic apparatus that functions as a display element, configured such that the light emission regions in the multiple wavelength light emitting device are formed as pixels for displaying images, and such that the drive of each pixel can be controlled in response to pixel information.
An invention that realizes the fourth object noted above is an interference mirror, configured so as to be able to partially reflect light of mutually differing wavelengths, and comprising a plurality of interference reflecting layers arrayed sequentially in the optical axis direction, and gap adjustment layers positioned between the interference reflecting layers.